docs: def _parse_text(self, el, refs=None, specials=None,  element_cls=Paragraph):
          """Like _parse_element but ensure a single element."""
          if specials is None:
              specials = {}
          if refs is None:
              refs = {}
          elements = self._parse_element_r(el, specials=specials, refs=refs, element_cls=element_cls)
          # This occurs if the input element is self-closing... (some table td in NLM XML)
          if not elements:
              return [element_cls('')]
          element = elements[0]
          for next_element in elements[1:]:
              element += element_cls(' ') + next_element
          return [element]